In an armature of a conventional electric motor, a coil-mounting tooth of a stator core has stepped surfaces at locations where a predetermined length portion of the tooth is narrowed from both its end surfaces in the axial direction of the stator core, whereby an insulator is fittingly fixed and a winding space is maximally provided (refer to Patent Document 1 and Patent Document 2, for example).
In another example, an insulator is fixed to both ends of a stator core without having a narrowed tooth as in the above description. A film insulator is disposed to provide insulation within a slot, and a folded portion of the insulator, where the insulator partially protrudes toward the inside of the slot, is provided to control the film insulator in the axial direction (refer to Patent Document 3, for example).